By the numbers, PS3 was behind the 360 by 5 million units as of last week (using these numbers too becuase they are easier :P). Here is the break down of how many more they would have to sell a week to beat the 360.
Years | # sold per week (over 360 sales) |
1 | 96,153.87 |
2 | 48,076.92 |
3 | 32,051.28 |
4 | 24,038.46 |
5 |
19,230.76 |
As you can see, it would have to sell a lot more then it usually does to pull these. It's doable I guess, but the system are usually so close that it would take 3-5 years to do this not including if the 360 beats the PS3 on any week. This is all based on the assumption that PS3 outsells the 360 every week for x number of years.